JP2894187B2 - Step-up power supply IC - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a step-up power IC.

[0002]

2. Description of the Related Art A step-up power supply device has been used as a power supply for portable electronic devices, such as small radios, tape players and CD players, which are supplied with power by a battery. The boosting power supply supplies boosted power so that a device such as a microcomputer IC incorporated in the electronic device and having a minimum operating voltage higher than that of the battery can be driven. In the simplest form, a booster power supply device includes a booster circuit and an oscillator coupled to and controlling the booster circuit. In the prior art, the oscillator is connected to a DC voltage source, which in the electronic device is a battery. When power is supplied by the voltage source and the oscillator is turned on, the booster circuit increases the voltage received from the voltage source to an integer multiple, such as two or three times the original voltage. FIG. 1 is a graph of the oscillation frequency and the power supply voltage of the CMOS oscillator. This graph shows that when the power supply voltage of the oscillator is low, the frequency of the oscillator decreases. According to the data of FIG. 1, when the power supply voltage is reduced from about 3 V, first, the oscillation frequency slightly increases to 0.1 V.
At 9 to 1 volt, the frequency peaks, and as the power supply voltage drops, the oscillation frequency begins to drop again.
The frequency of the oscillation is important because the oscillator emits noise. The maximum audible frequency that can be heard by the human ear is about 20 kHz
z. As shown in FIG. 1, when the power supply voltage of the oscillation circuit is 1
In the region above V, the oscillation frequency is higher than 20 kHz, so that the noise is outside the audible range. However, when the power supply voltage decreases and the oscillation frequency decreases, the noise enters the audible range. The audible noise emanating from the oscillator impairs the desired transmission of the small player. As can be seen on the left side of FIG. 1, the drop in frequency is caused by a drop in battery voltage. Even though the battery has sufficient power to continue supplying power to the electronics, the noise caused by the low power results in an undesirable sound and the battery must be replaced.

[0003]

With the conventional method of powering the oscillator, the battery forming the voltage source is not efficiently used. When the frequency of the oscillator falls to the audible range and interferes with the quality of the output of the electronics player, the battery must be replaced. This is an inefficient use of batteries as there is still enough power to operate the electronics without this problem.

[0004] What is needed is a way to maintain the frequency of the oscillator above the audible range by utilizing the total power stored in the power supply. At the same time, the power consumed by the oscillation circuit must be able to be kept low during the standby period.

[0005]

SUMMARY OF THE INVENTION As contemplated by the present invention, a simple means for increasing the power supplied to an oscillator to maintain the oscillation frequency above the audible range is to use the output of the booster circuit to control the oscillator. This is achieved by supplying a power supply voltage to the The voltage from the booster circuit is increased by a certain factor and fed back to the oscillator. Thus, the power supply does not lower the oscillation frequency to within the audible range even if it falls below the 0.9 V cutoff level shown in FIG.
The supply of the power supply voltage from the booster circuit is used only during the operation mode of the electronic device to prevent the oscillation frequency from lowering. During standby mode, the oscillator is connected directly to the power supply to save power consumption of the oscillator.

[0006]

A major advantage of the present invention, in addition to other advantages, is the extended life of the power supply. Even if the power supply drops to a level that causes noise in the oscillator, it still has the power to operate the electronics. By feeding back the output from the booster circuit as a power supply voltage into the oscillator, the oscillation frequency of the oscillator is maintained above the audible range, and the power supply can be used for a longer time. The power supply will be used more efficiently.

[0007]

FIG. 2 shows an embodiment of the present invention, wherein 1 denotes a booster power supply IC, and 2 denotes an oscillator for driving a booster circuit 3. 4 represents a power supply or a battery Vcc, and 5 represents a switch. When the output voltage of the battery 4 starts to decrease, especially when the output voltage decreases to less than 0.9 V, the oscillation frequency of the oscillator 2 decreases to 20 kHz or less. This frequency is recognized as an audible frequency that can be heard by human ears. This is important in portable sound systems, such as battery-powered radios and portable tape or disc players, as they emit unwanted sounds.

[0008] Generally, batteries used in portable radios or tape / disk players have a 1.5V power supply. During the life of the battery, the power gradually diminishes. At about 0.9V, the battery still has enough power to keep the portable unit running. However, frequencies generated at voltages below about 0.9V cause undesirable noise.

As can be seen in FIG. 2, oscillator 2 can draw power from two different power sources through switch 5. During the full operation mode (A side of the switch 5), the oscillator 2 draws power from the booster circuit 3 or Vo. The Vo output of the booster circuit 3 is obtained by multiplying VCC by a predetermined coefficient a, that is, Vcc (a). Here, a is an integer. In a preferred embodiment, the booster circuit 3 sets Vcc to 2
Therefore, the power supplied to the oscillator 2 becomes 2 × Vcc. Referring to FIG. 1, it can be seen that twice Vcc is supplied to the oscillator 2. As the voltage rises in the graph, the frequency peaking at about 1.0 volt gradually begins to fall. If the voltage is too high, the oscillator 2 will enter the audio frequency.
The frequency must be maintained above 20 kHz.
With a 1.5V battery, doubling the voltage keeps the frequency well above 20kHz. When the booster circuit 3 increases the power supply voltage more than twice, FIG.
Curve goes into the audible range as the voltage increases, so the possibility of audible noise increases. To this end, the preferred embodiment is to increase Vcc by a factor of two.

A two-fold increase in Vcc allows the battery 4 to be replaced after it has dropped to about 0.45V.

The second power from which the oscillator 2 draws power is supplied directly from the battery 4 through the B side of the switch 5. It is possible to always draw power from the booster circuit 3 whose power is twice Vcc. However, if twice the power is constantly drawn even during the standby mode, the power stored in the battery 4 will quickly disappear. Since the portable radio or tape / disk player is in standby mode most of the time, it is inefficient to continuously drain and waste power from the battery 4. Therefore, switch 5
Thus, the oscillator 2 can be pulled out from Vcc during the standby mode, and the power stored in the battery 4 is saved.

The switch 5 is supplied with an external switch control signal instructing the switch 5 to switch from the standby mode to the full operation mode.

FIG. 3 shows an embodiment of the switch 5 and the oscillator 2. A detailed description of oscillator 2 is outside the scope of the present invention and is not necessary for understanding the present invention. Therefore, in FIG. 3, only the circuit example of the oscillator 2 is illustrated.

The switch 5 is 2 in the preferred embodiment.
MOS gates 10 and 11 are used. Node 12 represents the external switch control signal input. Node 14 is the connection for Vcc. The node 13 is a connection part of Vo. When a low signal indicating the full operation mode is received at the node 12, the MOS gate 10 is turned on, and power flows from the booster circuit 3. When the high signal is received at the node 12, the MOS gate 10 is turned off and the MOS gate 11
Turns on. At this time, power from the battery 4 flows to the oscillator 2.

FIG. 4 shows the PMOS-PMOS setting of the switch 5. In this setting, the node 12 branches to two input signal paths 12a and 12b. Lo of node 12a
The w signal carries power from node 13 or Vo. Similarly, FIG. 5 shows the NMOS-NMOS setting of the switch 5. In FIG. 5, the high signal at node 12a carries power from node 13 or Vo.

In the preferred embodiment, other combinations of MOs
An S gate and an external control signal can also be used.

[0017]

As described above, coupling the oscillator to the output of the booster circuit of the booster IC increases the usefulness of the DC power supply or battery. Supplying power to the oscillator using power from the booster circuit prevents the oscillation frequency of the oscillator from falling within the audible frequency range. The life of a battery that still has the power to operate a portable radio or tape / disk player will be much longer. Further, by switching a switch coupled to the oscillator, the oscillator is directly coupled to the battery source during the standby period. This extends the life of the battery.

[Brief description of the drawings]

FIG. 1 is a graph of a power supply voltage and an oscillation frequency of an oscillator according to the present invention.

FIG. 2 shows components of a boost power supply IC improved according to the present invention.

FIG. 3 is a preferred embodiment of a switch coupled to an oscillator according to the present invention.

FIG. 4 is another embodiment of the switch of FIG. 3 according to the present invention.

FIG. 5 is another embodiment of the switch of FIG. 3 according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Step-up power supply IC 2 Oscillator 3 Step-up circuit 4 Power supply or Vcc 5 Switch 10 MOS gate 11 MOS gate 12 External signal node 13 Node connected to Vo 14 Node connected to Vcc

Claims (2)

(57) [Claims] 1. A booster power supply IC coupled to a voltage source, comprising: a booster circuit coupled to the voltage source for boosting and outputting a voltage from the voltage source; and a booster circuit coupled to the booster circuit. An oscillator for controlling the operation of the booster power supply IC; and coupling the oscillator to a first node when the booster power supply IC is in a standby mode, and coupling the oscillator to a second node when the booster power supply IC is in an operation mode. A switch, wherein the first node is coupled to the voltage source and the second node is coupled to an output of the booster circuit. 2. A boosting power source I having an oscillator and a boosting circuit.
A method for saving power in C, comprising: directly coupling an oscillator to a voltage source during a standby mode to obtain power from the voltage source to drive the oscillator;
And coupling an oscillator to the output of the booster circuit during an operating mode to obtain power for driving the oscillator from the output of the booster circuit.